Building Blocks Of Nervous System

Question 0

Dendrites

Answer 0

Branched part of neuron that receives impulses and conducts them toward cell body.

“Input” side of neuron
Receives the impulses from many other neurons
Dendrites are typically short ( few hundred microns)

Question 1

Neurons

Answer 1

Specialised cell in the nervous system that accumulates and transmits information
3 parts : dendrites, cell body(soma), axon

Come in different shapes and sizes
Cell body has diameter between 5-100microns

Question 2

Cell body (soma)

Answer 2

Portion of the neuron containing the metabolic machinery that keeps the cell alive and functional

Contains neurons nucleus

Question 3

Axon

Answer 3

Part of neuron that transmits impulses to glands, muscles and other neurons
Axons are much longer than dendrites
Longest axons are in motor neurons
The “output” side
Extends outward from cell body like whisky thread and may branch at the end.

Question 4

Efferent neuron

Afferent neuron

Answer 4

Efferent neurons are nerves that carry messages outward from the central nervous system. (Generally info from brain to destination outside brain)

Afferent neurons are nerves that carry messages inward toward the central nervous system.( keep nervous system informed about external world and body’s internal environment)
Some afferent are attached to specialised receptor cells that respond to external energy changes such as light, temp, pressure ect.
These receptor cells transduce the physical stimuli into electrical changes which trigger a nervous impulse in other neurons

Question 5

Interneurons

Projection neurons ( sometimes referred to as interneurons also)

Answer 5

neurons that are neither afferent nor efferent but instead carry information from one neuron to another ( make connections within CNS)

Account for 99% of neurons

Projection neurons = link rea of CNS to another perhaps distant area
To perform this function they typically have long axons

Interneurons = make local connections within nervous system, have short or no axon at all.

Question 6

Glia

Answer 6

Type of cell in nervous system long believed to provide a “support” function for neurons; recent research indicates that glia provide many other functions as well.

Many more glia than neurons

Broad set of functions -
Provide nourishment for neuron and key role in controlling nutrient supply - glucose is main fuel for nervous system but most energy neuron uses does not come from glucose directly instead glia convert glucose into lactate that feeds neuron.
Glia are sensitive to activity level in each neuron and increase blood flow ( providing more O2 and fuel) whenever the neurons in area become more active.
Key in brain development also ( before birth and in first months) brain grows at fast rate and cells. Rapidly reproduce and differentiate, newly created neurons migrate from one position in brain to another. This migration is guided by glia ( act as guidewires)
Once neurons reached destination and established appropriate connections the glia cells produce. Chemicals to shut down process of neural growth.
Glia ensure stable pattern of connections.

Question 7

Myelin

Answer 7

Fatty substance that makes up some type of glial cells; these cells wrap around the axon of some neurons, providing an insulting “myelin sheath” around these neurons.

Insulating sheath of myelin has gaps = nodes of ranvier between myelin cells.
Increases speed of neuronal communication
Especially important in longer axons that span longer distance and thus need greater transmission speed.
Crucial is the gaps (NOR) and it is the combination of wrappers and gaps that speeds up the nerve impulses travelling along myelinated axons
Myelin is white
White matter in brain consists of myelinated axons
Grey matter is cell. Bodies, dendrites and unmuelinated axons.

Question 8

Action potential

Answer 8

A brief change in the electrical charge of neuronal membrane; the physical basis of the signal that travels the length of the neuron.

Neurones membrane is highly sensitive to stimulation.
Stimulate it electrically,or chemically and neuronal membrane changes its structure, producing cascade of changes that can lead to Electrical signal called action potential.
AP involves electrical changes - to study these can insert micro-electrode into a neurones axon and place second electrode on axons outer surface - allows us to measure electrical activity near cell membrane - tells us that even when neurone not being stimulated there is voltage difference between inside and outside of cell.
Difference of -70 millivolts
Because this difference occurs when neuron is stable it is called the resting potential.

Question 9

Resting potential

Answer 9

The voltage difference between the inside and outside of a neuronal membrane when the neurone is not firing.
About -70millivolts

Question 10

Excitation threshold

Answer 10

The voltage difference between a neurons interior and exterior that,if exceeded causes the neuron to fire.

To find out what happens when neurone stimulated can apply 3rd micro electrode to apply brief electrical pulse to outside surface of cell. This pulse reduces voltage difference across membrane.
If pulse is weak may reduce voltage difference a little but membrane maintains integrity and quickly restores resting potential (-70)
But if pulse strong enough to push voltage difference beyond critical excitation threshold ( about -55millivolts) then this leads to action potential.
In that region of cell the voltage difference between inside and outside membrane collapses to zero 0 and begins to reverse itself .
Inside of cell no longer negative compared to outside instead suddenly swings positive ( up to +40) this momentry change is the action potential.
It’s short lived and resting potential is restored.

Question 11

Refractory period

Answer 11

The time after an action potential during which a neurons cell membrane is unprepared for the next action potential.

Question 12

Depolarise

Answer 12

In the nervous system, to lose the charge that normally exists across the neuronal membrane.

Question 13

Propagation

Answer 13

The spread of the action potential down an axon, caused by successive changes in electrical charge along the length of the axons membrane.

Question 14

All or none law

Answer 14

The law that all action potentials have the same strength and speed regardless of the triggering Stimulus.

More intense stimuli excite more neurons as neurons vary in their excitation thresholds.
When neurons bombarded with sustained stimulus they fire action potentials , more than once , they generate a stream of AP by mean of repeated destabilisation and re stabilisation
All or one law applies within this stream or volley.
Different neurons have different max rates of firing.

Question 15

Synapse

Answer 15

The small gap between 2 adjacent neurons, consisting of the presynaptic and post synaptic neurons membranes and the space between them.

The neural signal has to move down a neurons axon jump across the gap then trigger the next neurons response.
Transmission across synapse slows down the neuronal signal but this setup has huge advantage - each neuron receives signals from many other neurons and this allows the receiving neuron to integrate into from many sources.
Also makes it possible for several weak signals to add together, eliciting response that the individual signals couldn’t achieve on their own.
Also communication at synapse is adjustable

Question 16

The synaptic mechanism

Answer 16

Neurones communicate across synapse chemically
Neurone on sending side releases certain molecules that drift across synapse and trigger response in receiving neurone.
This is different to the electrical signalling occurring within each neurone.

Question 17

Otto Loewi research on frog hearts

Answer 17

He knew that activity in vagus nerve decreased heart rate.
Hypothesised that nerve communicates with heart by releasing chemical.
To test this he dissected hearts out of 2 frogs and placed each with nerve attached in fluid filled jar
Electrically stimulated one of the vagus nerves and the attached heart immediately slowed heart rate.
Loewi then took sample from that container and put it in the other container with the second heart in.

If signal was electrical then this would have no effect
If chemical though some of the molecules would diffuse into the fluid and slow the second hearts heart rate. - this is what happened

Question 18

Neurotransmitters

Answer 18

Chemicals released by one neuron (usually presynaptic neuron), which triggers a response in another neuron ( usually post synaptic neuron); the chief means of communication among neurons.

Question 19

Presynaptic neuron

Answer 19

The transmission process begins in the presynaptic neurons tiny axon terminals. Within these swellings are many tiny sacs ( synaptic vesicles) filled with neurotransmitters.
When presynaptic neuron fires some of the vesicles burst and eject contents into the gap.

Question 20

Post synaptic neuron

Answer 20

The neurotransmitters diffuse across gap and attach to receptors on membrane of post synaptic membrane.
This sequence causes certain ion channels to open or close.

There are several types of neurotransmitters, each with different effects on the post synaptic cell.

Question 21

Synaptic re uptake

Answer 21

The presynaptic neurons process of re absorbing its own neurotransmitters after signalling

Question 22

Neurons are selective

Answer 22

Individual neurons are selective in what neurotransmitters they respond to ( many are responsive to more than one).
Each neuron has its own pattern of sensitivities.
Thus in each part of brain nervous system can use one transmitter to send one type of message and different transmitter to send different type of message.

Question 23

Acetylcholine ( ACh)

Answer 23

Released at many synapses and at the junction between nerves and muscles; release of ACh cause muscle fibres to contract

Question 24

Serotonin (5HT)

Answer 24

Involved in mechanisms of sleep,mood, and arousal

Question 25

Gamma amino butyric acid (GABA)

Answer 25

Most widely distributed inhibitory transmitter of the CNS

Question 26

Glutamate

Answer 26

Major excitatory transmitter in brain; plays crucial role in learning and memory

Question 27

Norepinephrine

Answer 27

Helps control arousal level; influences wakefulness,learning and memory.

Question 28

Dopamine

Answer 28

Influences movement,motivation,emotion

Question 29

Lock and key model

Answer 29

Proposes transmitter molecules will affect the post synaptic membrane only if the molecules shape fits precisely into the receptor.
Highly simplified account account of the dynamics linking transmitters to receptors.

Question 30

Agonists

Answer 30

Drugs that enhance a neurotransmitters activity.

Question 31

Antagonists

Answer 31

Drugs that impede activity of neurotransmitter

Question 32

How do agonists work

Answer 32

They exert influence in many ways:

1) mimic transmitter - so can activate receptors on their own.
2) block re uptake of neurotransmitter into presynaptic cell.
3) counteract cleanup enzymes that break down transmitter after its triggered response.
4) promote production of transmitter (usually by increasing availability of some chemical needed for the transmitters manufacture)

2 & 3 both have effect of leaving more transmitter within synaptic gap, increasing transmitters opportunity to influence postsynaptic membrane.
So it increases the strength and duration of transmitters effect.

Question 33

How do antagonist work?

Answer 33

Antagonists prevent transmitter working by :

1) binding to the synaptic receptor and blocking off the transmitter
2) speeding up reuptake of transmitter
3) augmenting cleanup enzymes

Question 34

Endogenous substances

Answer 34

Many agonists and antagonists depend on endogenous substances.
They are substances produced naturally in body and provide a way for the nervous system to modify and control its own functioning.

E.g. Endorphins = family of chemicals produced inside brain that influence how we perceive and cope with pain.
These naturally produced painkillers influence brain in much the same way as morphine.

Question 35

Exogenous substances

Answer 35

Neurotransmissiin can also be modified by exogenous agonists or antagonists.
These are chemicals introduced from outside the body.
Can be difficult to get these substances into the brain.
The cells that make up nervous system are extremely sensitive to toxins so they are protected by the blood brain barrier.

Question 36

Blood-brain barrier

Answer 36

Specialised membranes that surround the blood vessels within the brain and filter harmful chemicals out of the brains blood supply.

Prevent toxins reaching CNS

This mechanism evolved to keep out toxins but it is also an obstacle for medications.
So medications need to be designed not only to have desired effect but also to be able to get through barrier.

Question 37

Cocaine

Answer 37

Agonist that blocks reuptake of dopamine, norepinephrine and epinephrine into presynaptic neurons.
Effect= arousal , restlessness, euphoria

Question 38

Antidepressants

Answer 38

Work in similar way to cocaine but block reuptake of serotonin

Question 39

Other drugs are antagonists

Answer 39

Medications for SZ for example block postsynaptic receptors.

Help patients control psychotic thinking.

Question 40

Communication through bloodstream

Answer 40

Nervous system also communicates through bloodstream by means of chemical messages.
Blood travels all around body so signals in bloodstream travel much longer distances.
This means of internal communication is called endocrine system.

Question 41

Endocrine system

Answer 41

System of glands that release secretions directly into bloodstream and affect organs elsewhere.

Various glands release chemical secretions (hormones) into bloodstream that travel and affect structures that are often far away from their chemical birthplace.

Hormones travel longer distances so their effect is sower but longer lasting

Although the blood travels all around the body and thus so do the hormones, they only detected at specialised receptors at particular locations. In this way endocrine system has well defined targets just like neurotransmitters.

Question 42

Hormones

Answer 42

Chemical released by a gland. Hormones travel through the bloodstream and influence functions such as metabolic rate,arousal level, and the livers sugar output.

Question 43

Single cell recording

Answer 43

Researchers monitor the moment by moment activity of individual neurons in the brain while placing various stimuli in front of the animals eyes.
This method has told us a lot about vision.

Question 44

Multi unit recording

Answer 44

Collects single-cell data from multiple neurons at the same time.

Uses micro electrodes to record activity of individual cells then relies on computer analyses to examine patterns of activity across the entire collection of cells.

Provides information about how each cell is influencing the others as well as information about the aggregate pattern of responding.

Question 45

Transcranial magnetic stimulation

Answer 45

The technique of applying repeated magnetic stimulation at the surface of the skull to temporarily stimulate or disable a target brain region.

Question 46

Electroencephalogram

Answer 46

A record of the brains activity recorded by placing electrodes on the scalp

Question 47

Event related potential

Answer 47

Electrical changes in the brain that correspond to the brains response to a specific event; measured with EEG.

Question 48

Limitation of TMS

Advantages of TMS

Answer 48

Only influences structures near the brain

But let’s investigators examine in detail the function of this brain region

More than just a research tool as it has therapeutic potential e.g. For treating clinical depression

Question 49

EEG advantages & disadvantages

Answer 49

High temporal resolution

Detects all brain activity so can’t distinguish local areas and ha to remove background noise

Question 50

CT computerised tomography

Answer 50

A technique for examining brain structure by constructing a composite of X-Ray images taken from many different angles.
Yields precise information about shape and position of structures in brain.

Question 51

MRI (magnetic resonance imaging)

Answer 51

A neuroimaging technique that documents the effects of strong magnetic pulses on the molecules that make up brain tissue. A computer then assembles this information into a picture of brain structure.
Can show healthy and unhealthy tissue so useful in diagnosis of tumours, blood clots etc.

Question 52

Con of MRI and CT scans

Answer 52

They provide precise anatomical information but can’t tell us the brains moment by moment functioning. E.g. What areas of the brain are more active at any given time.

Question 53

PET (positron emission tomography)

Answer 53

Technique for examining brain function by observing the amount of metabolic activity in different brain regions.

Pops is injected with safe dose of an radioisotope - often an isotope of a sugar that resembles glucose, the brains metabolic fuel.
The pet scan then keeps track of how this radioactivity is distributed across the brain.
Brain cells that are more active at a given time will need more glucose and so absorb more radioactivity.
So by tracking pattern of radioactivity can know where glucose is being used more and hence know what brain regions are more active.

Question 54

Functional MRI (FMRI) scan

Answer 54

A technique for examine brain function by measuring blood flow and oxygen use within the brain.

If adapts standard MRI scans to study brain activity.

FMRI scans rely on the fact that haemoglobin is less sensitive to magnetism when it is transporting oxygen
By tracking Hb researchers can measure the ratio of oxygenated to deoxygenated blood - this ratio yields a measurement called the blood-oxygenation-dependant signal. (BOLD).
When neural regions more active then the ratio increases because the tissue is demanding more oxygen. So we can track brain activity.

Question 55

Advantage of FMRI over PET scans

Answer 55

Spatial precision
Temporal precision

Pets scans summarise brain activity over period of about 40 seconds but the BOlD provides measurements across just a few seconds.

EEG yields even more precise temporal information but unlike FMRI it cannot tell us exactly where in the brain the activity is taking place.

Question 56

The power of combining techniques

Answer 56

Each technique for analysing the brain has limitations and advantages some tell us about the activity of brain but not location of activity and vice versa others tell us about shape and structure.

Question 57

Central nervous system

Answer 57

The brain and spinal cord

Question 58

Peripheral nervous system

Answer 58

The afferent and efferent nerves that extend from the brain and the spinal cord to connect them with the muscles and organs.

Nearly all the peripheral nerves connect to the CNS by the spinal cord and this is why it’s so important the cord is protected by the bones and connective tissue of the spine and why damage to the spinal cord is so serious.

Question 59

Somatic nervous system

Answer 59

The division of the peripheral nervous system that controls the skeletal muscles and transmits sensory information

Question 60

Autonomic nervous system

Answer 60

Division of the peripheral nervous system that receives information from and controls the internal organs.

Question 61

Sympathetic branch

Answer 61

Division of the autonomic nervous system ( which is part of the peripheral nervous system) that mobilizer the organism for physical exertation.
E.g. Gets them ready for action

Question 62

Parasympathetic branch

Answer 62

Division of the autonomic nervous system that restores body’s normal resting state and conserves energy.

Question 63

Brain stem

Answer 63

Region of brain at the top of the spinal cord

Includes the medulla and pons

Question 64

Cerebellum

Answer 64

Part of brain that controls muscular coordination and equilibrium.

Question 65

Cerebral cortex

Answer 65

Outermost layer of the forebrain

Thin covering but there is great deal of cortical tissue.
This is possible because it’s crumpled up and jammed into the limited space inside the skull.
Crumpling produces the obvious convolutions that cover brains outer surface.

Question 66

Cerebral hemisphere

Answer 66

One half (left or right) of the cerebrum, the topmost part of the brain

Question 67

Frontal lobe

Answer 67

Area at front of each cerebral hemisphere

Includes tissue crucial for many aspects of planning and controlling thoughts and behaviour.

Question 68

Parietal lobe

Answer 68

Area in each cerebral hemisphere that lies between the frontal and occipital lobes;
Includes tissue crucial for receiving information for receiving information from the skin senses.

Question 69

Temporal lobe

Answer 69

Areas in each cerebral hemisphere lying below the temples

Includes tissue crucial for hearing and many aspects of language use.

Question 70

Occipital lobe

Answer 70

Rearmost area of each cerebral hemisphere

Includes tissue crucial for processing visual information

Question 71

Medulla
Pons

Both parts of the brain stem

Answer 71

Medulla -
at bottom of brain stem, controls breathing, blood circulation, helps us maintain our balance.

Pons-
Above the medulla
Important in controlling brains overall attentiveness and help govern timing of sleeping and dreaming.

Question 72

Midbrain

Thalamus

Both also part of brain stem above the pons

Answer 72

Both serve as relay stations directing information to the forebrain (where the info is more fully processed)
Have other roles also though:

Midbrain:
Regulate experience of pain
Key role in modulating our mood and shaping our motivation

Question 73

Forebrain ( largest part of brain that usually seen in photos)

Answer 73

Sits on top of brain stem

Outer layer of forebrain is the cerebral cortex and its this that you would usually see in photos.